The 5th-generation (5G) mobile communication technology new radio (NR) is a newly proposed topic by the 3rd Generation Partnership Project (3GPP) organization. As the new generation of 5G technology is further discussed, on the one hand, since the communication system is backward compatible, the new technology developed later tends to be compatible with the standardized technology; on the other hand, since there are a large number of existing designs in the 4th generation mobile communication (4G) technology LTE, a flexibility of 5G will be seriously affected for the sake of compatibility, thus degrading its performance Therefore, at present, 3GPP organization is focusing on parallel studies in two directions, where a technology discussion group that does not consider the backward compatibility is called 5G NR.
In a multi-beam (analog beamformed) system currently discussed by 5G/NR, different beams correspond to different directions and different coverage areas.
Correspondingly, a user equipment selects its preferred downlink transmission beam (DL Tx Beam) by measuring channel state information reference signals (CSI-RS) carried on different beams, and when performing random access, the user equipment needs to inform a network of its selected DL Tx Beam. For the random access, a current conclusion from 3GPP RANI is as follows: system information indicates different physical random access channel (PRACH) resources and/or preamble indices for different DL Tx Beams, that is, PRACH resources and/or preamble indies are divided into groups, and different PRACH resources and/or preamble index subsets correspond to different DL Tx Beams. There are already conclusions supporting that connected user equipments select the preferred DL Tx Beam by measuring the measurement result of the configured CSI-RS.
At present, a resource indicator of CSI-RS is used for the configuration, indication and identification of the CSI-RS in the NR system. In the NR system, the number of CSI-RSs supported by the next generation base station (gNB) is very large. If PRACH resources and the preamble index subsets of the downlink transmission beam are used for direct association of the CSI-RS resource indicator, the base station needs to send indication information with a large amount of data to the user equipment to indicate on which resources the user equipment measures the CSI-RS, and signaling overhead of such indication is relatively high, resulting in a waste of more system resources.